1. Technical Field of the Invention
The present invention relates to an apparatus and method for generating power utilizing a Thermo-Electric Generator (TEG) to convert thermal energy generated by rotation of a bearing within a bearing housing into electric energy.
2. Background Art
Bearings are used to support many rotating objects. Bearings are commonly integrated into a variety of machines. The bearings are a key factor contributing to the reliability of the machine. The system designed commonly installs one or more bearing condition monitoring devices to ensure the bearings remain in working order. The majority of the condition monitoring devices requires low voltage electrical power for operation. Some systems include other components that also utilize electrical power. One such electrically operated component can be a communication device for transferring the condition monitoring information to a remote service company.
Bearings can be integrated into many different machines having a wide variety of applications. The applications can be deployed at very remote, rural locations, commonly void of utility provided power.
Batteries provide a limited capacity, which dictates a limited supply and thus a limited run time. Obtaining power from a commercial utility source can be costly, particularly for remote installations. Transferring electrical power from a commercially available source can require running extensive and costly power cabling and support equipment. Maintenance of these systems must be considered. Replacement of batteries incurs both parts and labor costs. These concerns are aggravated for temporary installations.
During operation, the bearing can generate a significant amount of heat. Bearing which generate a significant amount of heat commonly include heat dissipation or thermal transfer systems. One exemplary thermal transfer system includes one or more integrated liquid cooling passages. Liquid coolant is pumped through the integrated liquid cooling passages extracting heat from the bearing or bearing assembly. The liquid coolant is passed through a heat exchanger to remove the extracted heat from the liquid coolant. The cooled coolant is returned to the bearing housing to repeat the heat extraction or thermal regulation process.
Thermo-Electric Generators (TEG's) are commonly available in a variety of form factors. They are available is a variety of different sizes and performance levels. Thermo-Electric Generators (TEG's) are offered utilizing either of two technologies: (a) normal thermo couples and (b) thin film technology.
Thermo coupled based Thermo-Electric Generators (TEG's) utilize a thermocouple consists of two conductors of different materials (usually metal alloys). Any junction of dissimilar metals will produce an electric potential related to temperature. The thermocouple produces a voltage in the vicinity of the point where the two conductors contact one another. The voltage produced is dependent on, but not necessarily proportional to, the difference of temperature of the junction to other parts of the respective conductors. Thermocouples are used in a variety of applications, including a temperature sensor, a device for converting a temperature gradient into electricity, and the like. Commercial thermocouples are inexpensive, interchangeable, are supplied with standard connectors, and can measure a wide range of temperatures. One advantage of a thermocouple over other methods of measuring a temperature is that thermocouples are self-powered.
A thermocouple can produce an electric current. The concept utilizes what is referred to as the Peltier effect. The Peltier effect is the presence of heat at an electrified junction of two different metals. When a current is made to flow through a junction composed of materials A and B, heat is generated at the upper junction at T2, and absorbed at the lower junction at T1. The Thermo-Electric Generator (TEG) applies the thermocouple in accordance with the reverse concept of the Peltier effect, whereby the presence of heat at the upper junction T2, and the presence of a reduced temperature at the lower junction at T1 the thermocouple generates a current.
The Thermo-Electric Generator (TEG) can utilize a series of thermocouples connected in series to form a thermopile, where all the hot junctions are exposed to a higher temperature and all the cold junctions to a lower temperature. The output is the sum of the voltages across the individual junctions, giving larger voltage and power output.
Thin film technology based Thermo-Electric Generators (TEG's) are fabricated utilizing Peltier cooler chips, or a generator based upon the Seebeck effect. The Thermo-Electric Generator (TEG) consists of leg pairs of n- and p-type material. Each leg pair generates a certain voltage. The voltage (U) generated by a Thermo-Electric Generator (TEG) is directly proportional to the number of leg pairs (N) and the temperature difference (ΔT) between top and bottom side times the Seebeck coefficient (α), where:U=N(times)ΔT(times)α.
The Seebeck effect is caused by two things: charge-carrier diffusion and phonon drag. Charge carriers in the materials will diffuse when one end of a conductor is at a different temperature from the other. Hot carriers diffuse from the hot end to the cold end, since there is a lower density of hot carriers at the cold end of the conductor, and vice versa. If the conductor were left to reach thermodynamic equilibrium, this process would result in heat being distributed evenly throughout the conductor. The movement of heat (in the form of hot charge carriers) from one end to the other is a heat current and an electric current as charge carriers are moving.
Recently developed thermoelectric devices are made from alternating p-type and n-type semiconductor elements connected by metallic connectors. Semiconductor junctions are common in power generation devices, while metallic junctions are more common in temperature measurement. Charge flows through the n-type element, crosses a metallic interconnect, and passes into the p-type element.
The thermoelectric device can be utilized in either of two applications: (a) utilizing power to control temperature and (b) utilize a thermal difference to generate electric power. In the first configuration, where power is provide the thermoelectric device provides a thermal generating device, utilizing the Peltier effect to act as a cooler. In this configuration, electrons in the n-type element move opposite the direction of current and holes in the p-type element will move in the direction of current, both removing heat from one side of the device. In the second configuration, where a thermal difference is applied to the thermoelectric device, the thermoelectric device functions as a power generator. The heat source drives electrons in the n-type element toward the cooler region, creating a current through the circuit. Holes in the p-type element then flow in the direction of the current. Therefore, thermal energy is converted into electrical energy.
Thermo-Electric Generators (TEG's) can also utilize other effects, including:
(A) The Ettingshausen Effect, which is a thermoelectric (or thermo magnetic) phenomenon that affects the electric current in a conductor when a magnetic field is present, and/or
(B) The Nernst effect, which is a thermoelectric (or thermo magnetic) phenomenon observed when a sample allowing electrical conduction is subjected to a magnetic field and a temperature gradient normal (perpendicular) to each other.
A variety of parameters are monitored to continuously determine a condition of a bearing. The application of the bearing may limit the availability or ease of providing electrical power to the sensors used to monitor the condition of the bearing. What is desired is a power generating system that can be integrated into the bearing assembly to harvest power from the bearing assembly and utilize the harvested power to generate electrical energy.